1. Field of the Invention
The present invention relates to the field of paging devices and, more particularly to a reliable and fast frame synchronization scheme for FLEX protocol paging devices.
2. Description of the Related Art
The use of paging devices has increased dramatically over the years. Paging allows a person to contact a user of a paging device even in situations where the user is not in close proximity of a telephone. Paging devices allow the calling party to leave a telephone number where the party can be reached and/or a textual message such as xe2x80x9cCALL TOMxe2x80x9d so that the purpose of the xe2x80x9cpagexe2x80x9d is apparent to the user.
Due to recent developments, paging is being performed at higher speeds and with increased data capacity. The developments are attributable to the FLEX paging protocol that has quickly become the industry standard. In addition, newly developed power management techniques designed for use with the FLEX protocol have increased the battery power-savings capability of the paging devices.
The power-savings result from the fact that a pager designed to operate with the FLEX protocol will remain in a dormant low-power xe2x80x9cstandbyxe2x80x9d mode for almost the entire time that the paging device is powered-on. Once every four minutes, the paging device xe2x80x9cwakes upxe2x80x9d from the dormant standby mode and determines if there are any incoming messages destined for that paging device. Any incoming messages are processed and the paging device resumes the standby mode. Older protocols required the paging device to continuously check for incoming messages which quickly reduced the life of the pager""s batteries. Battery savings is a major concern in the paging industry and the FLEX protocol increases the battery savings of paging devices.
Referring to FIGS. 1 and 2, the paging device can remain dormant for long periods of time because the FLEX protocol uses a synchronous time-slotted frame format having a data-frame cycle 10 lasting four minutes. Each cycle 10 contains one hundred and twenty-eight data packets or frames 20 that are transmitted once during each cycle 10. Each frame 20 lasts approximately 1.875 seconds and has a preferred base data rate of 6400 bits per second. The FLEX protocol also supports data rates of 1600 and 3200 bit per second.
Each frame 20 contains a first bit synchronization portion 22 (hereinafter referred to as xe2x80x9cbit sync #1xe2x80x9d), first rate information portion 24 (hereinafter referred to as xe2x80x9crate info #1xe2x80x9d), second bit synchronization portion 26 (hereinafter referred to as xe2x80x9cbit sync #2xe2x80x9d), second rate information portion 28 (hereinafter referred to as xe2x80x9crate info #2xe2x80x9d) and eleven message block portions 30.
As shown in FIG. 2, bit sync #1 is a 32-bit pattern comprising alternating 1""s and 0""s. Bit sync #2 is a 16-bit pattern comprising alternating 0""s and 1""s. Rate info #1 is a 32-bit pattern containing the data rate of the frame while rate info #2 is a 32-bit pattern containing the complement of rate info #1. As is known in the art, the message blocks 30 contain the address of the pager that will receive the message and message information.
In general, each paging device is assigned a frame 20 within a cycle 10. To determine if the paging device has an incoming message, the paging device must wake up and synchronize itself to its assigned frame 20. Once synchronized, the paging device checks the remainder of the frame to determine if there is an incoming message destined for the address of the paging device. If there is no incoming message, the paging device resumes its standby mode. If there is an incoming message, the paging device processes the message and then resumes its standby mode. The process is repeated once every four minutes, i.e., once every cycle.
FIG. 3 illustrates the synchronization process 60 currently performed by conventional paging devices. The process 60 begins by reading a bit input from the assigned frame (step 62) and updating the last thirty-two input bits with the new input bit (step 64). A bit-by-bit comparison is made between the last thirty-two input bits and the bit sync #1 pattern (step 66) to determine a number of matches between the two. Once the number of matches between the last thirty-two input bits and the bit sync #1 pattern is obtained, it is determined if the number of matches is greater than or equal to a predetermined threshold T (step 68). Since the input bits may be corrupted by noise or other adverse conditions, a threshold T less than thirty-two is typically used. If the number of matches is greater than or equal to the threshold T, the frame is in sync (step 70) and the process 60 is complete. Upon completion of the process 60, further message processing is performed by the paging device. If the number of matches is not greater than or equal to the threshold T, the process continues at step 62 where the next input bit is read and the process 60 continues until there is a frame synchronization (at step 70).
The synchronization process 60 is not without its shortcomings. For example, the bit-by-bit comparisons used to determine whether there is a match between the input bits and the bit sync #1 pattern are made using xe2x80x9chard-decisionxe2x80x9d bits (that is, the decision is based on 1""s and 0""s). The bit-by-bit comparison resulting in the number of matches between the bit sync #1 pattern and the input data is performed using the hard-decision numbers means that any incorrect hard-decisions values will corrupt the number of matches. Thus, the process 60 is not too reliable. Accordingly, there is a desire and need for a reliable frame synchronization scheme for a paging device utilizing the FLEX paging protocol.
In addition, the process 60 is currently implemented in the software controlling the paging device. The hard-decisions and the bit-by-bit comparisons used to determine the number of matches between the input bits and the bit sync #1 pattern require numerous programming operations. The numerous programming operations slow down the processing required to perform the frame synchronization.
The reliability of the conventional frame synchronization process 60 can be improved by further considering bit-by-bit comparisons and the number of matches between the input data and the bit sync #2 or frame info patterns. These additional matches, however, add additional programming operations and processing time to the frame synchronization and would be inefficient. An inefficient and slow frame synchronization scheme is undesirable. Accordingly, there is a desire and need for a reliable frame synchronization scheme for a paging device utilizing the FLEX paging protocol that can be performed quickly and efficiently.
The present invention provides a reliable frame synchronization scheme for a paging device utilizing the FLEX paging protocol.
The present invention also provides a reliable frame synchronization scheme for a paging device utilizing the FLEX paging protocol that can be performed quickly and efficiently.
The above and other features and advantages of the invention are achieved by providing a method and apparatus that utilizes soft outputs from a paging device demodulator to perform frame synchronization. The soft outputs are summed after being correlated to a first pattern associated with a paging protocol. The summation is then compared to a frame synchronization threshold. Frame synchronization occurs when the summation reaches the threshold. Using soft outputs, and a summation of the outputs based on a correlation with the first pattern, the method and apparatus require less processing, are more efficient and are more reliable than conventional synchronization schemes.